1. Field of the Invention
The present invention relates to an image forming apparatus for performing image processing on image data and printing out the processed image data on a sheet, and, more particularly, to an inspection apparatus and an inspection method for reading an image printed on a sheet and determining whether the image has a predetermined print quality.
2. Description of the Related Art
Conventional printing and binding systems, such as print on demand (POD) machines, are provided with a mechanism for determining whether an image formed on a sheet after printing has a desired quality. Systems equipped with such a mechanism are called inspection systems, and include offline inspection systems and inline inspection systems as embodiments thereof. The offline inspection system is configured to form image data on a sheet, output the sheet to the outside of an image forming apparatus, and then pass the sheet through an image quality inspection device apart from the apparatus. On the other hand, the inline inspection system is configured to read image data formed on a sheet by an image forming apparatus by using an inspection sensor included in the apparatus and to compare the read image data with image data to be printed (input image data) for inspection. For instance, a density difference between the input image data and the image data read by the inspection sensor is calculated. Then, an area having a density difference that is equal to or greater than a threshold determined according to attributes of a recording medium, such as a type or thickness thereof, is specified as an error area (see Japanese Patent Laid-open No. 2009-78457).
In inspection processing (inspection determination), however, it is difficult to increase the performance of the inspection system even by using the density difference between the input image data and the image data read by the inspection sensor for the purpose of reducing an influence of show-through on an inspected product. This is because it is impossible to determine whether the generated density difference is a density difference depending on show-through or a density difference depending on a print defect included in the image formed on a sheet in printing. While high speed printing is available in most of the printing and binding systems, such as POD machines, the inspection processing under the influence of show-through may cause a significant decrease in system productivity due to the frequent occurrence of inspection errors. Further, various types of paper are used in the printing and binding systems, and accordingly, degrees of show-through vary widely. Setting a lower standard for inspection processing for the purpose of reducing the influence of show-through for every paper type may degrade inspection accuracy in inspecting images including print defects.